Low-cost Cu-based shape memory single crystals obtained by abnormal grain growth showing excellent superelasticity

Metal single crystals are generally obtained by directional solidification with sophisticated equipment and process. This method is not only very expensive but also very time-consuming. In this study, we report a new approach to produce Cu-Al-Mn-Mo shape memory alloys with single crystals through annealing cast polycrystalline alloys. The microstructure of the cast alloys has a common characteristic that the L2(1)-Cu2AlMn parent is completely coherent with bcc A2(Mo) precipitates due to bcc phase separation. The dissolution of bcc A2(Mo) nanoparticles during annealing process results in abnormal grain growth because of the formation of a continuous misorientation gradient within the grains. The single crystals obtained from large grains exhibit excellent superelasticity. When the orientation of single crystals is close to [-210], the largest full superelasticity is up to 10%, and the largest superelastic strain is up to 6.7%. It is expected that such microstructural design can also be applied to the production of large grains and even single crystals of other alloy systems with phase separation.